A heat-sensitive recording system is generally known in which a thermal head is brought into close proximity to the surface of a heat-sensitive recording material comprising a heat-sensitive coloring layer as provided on a support and scanned thereover so as to transfer the heat energy of the thermal head to the heat-sensitive coloring layer directly, or indirectly through an intervening protective layer thereby, to record or form a colored image on the heat-sensitive recording material. For instance, this technology has application to facsimiles or printers. However, in such a heat-sensitive recording process where a thermal head is closely attached to a heat-sensitive recording material and is scanned thereover, various problems often are encountered in that a faithful image could not be recorded, or the thermal head would be broken since the thermal head is abraded and worn, or the constituents of the heat-sensitive recording material adheres to the surface of the thermal head. Additionally, in the above heat-sensitive recording system using a thermal head, high-speed control in heating and cooling the heating element or elevation of the heating element density is limited because of the structural characteristic of the thermal head itself. Therefore, realization of high-speed recording or high-density and high-quality recording is often difficult in the heat-sensitive recording system.
On the other hand, in order to overcome the above-mentioned problems in the heat-sensitive recording system using a thermal head, employment of a laser beam to effect high-speed and high-density heat-recording without the need for contact between the energy source and the heat-sensitive recording material has been proposed.
One of the proposed techniques is to directly irradiate a heat-sensitive coloring layer with a laser beam to form an image thereon. In general, since the heat-sensitive coloring layer could hardly absorb visible rays and infrared rays, the technical matters relating to how the laser could be absorbed efficiently by the heat-sensitive coloring layer and to how the absorbed heat energy could be utilized efficiently in the coloring reaction are important themes addressed in the technical development of the image-forming process technology. For instance, various techniques concerning the image-forming process have been described in JP-A-50-23617, JP-A-54-121140, JP-A-57-11090, JP-A-58-56890, JP-A-58-94494, JP-A-58-l3479l (corresponding to U.S. Pat. No. 4,510,512), JP-A-58-l45493 (corresponding to U.S. Pat. No. 4,510,512), JP-A-59-89l92 (corresponding to U.S. Pat. No. 4,529,992), JP-A-60-205l82 and JP-A-62-56l95 and WOP86073l2A. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) However, in carrying out these illustrated proposals, heat energy necessary for coloration could be obtained only where the output power of the laser is relatively high in magnitude. As a result, it was extremely difficult to prepare a compact and inexpensive apparatus for carrying out the proposed methods. In addition, since the laser ray-absorbing substance to be contained in the heat-sensitive coloring layer is colored in accordance with the illustrated proposals, there is still another problem that the image to be recorded is a low-contrast and low-quality one. In general, most light-absorbing substances are inorganic compounds. However, almost all of them have a low light-absorbing efficiency. On the other hand, organic compounds which have a high light-absorbing efficiency and which have softer colors have not been developed to date.
On the other hand, as still another proposal for overcoming the above-mentioned problems in the prior art heat sensitive recording system methods, WOP8804237A has proposed a means of separating a laser ray-absorbing layer from and image-forming layer. In accordance with this proposed approach, a carbon black, which is recognized to have a good laser ray-absorbing efficiency, is employed whereby the laser ray-absorbing efficiency is elevated, and the irradiated carbon black is transferred onto the synthetic polymer film as fused because of the generated heat. That is, carbon black serves as both the light-absorbing substance and the image-forming substance in this technic. However, this technic has the drawback in that a large amount of heat energy is required for purposes of fusing the synthetic polymer film, and, therefore, a low-power laser is ineffective in practicing this technic.
As mentioned above, various high-speed and high-density heat-sensitive recording materials which may be heat-recorded by use of a laser beam without the need for contact between the material to be recorded and the energy source have heretofore been proposed. However, an image-recording system capable of being effected by the use of a low-power laser had not been proposed prior to the present invention.